The present invention relates generally to portable wireless communications systems, and more particularly to an improved coupling device used with such communication systems.
Wireless communications systems are in wide use. These systems are used to transmit both voice and data over cellular and other communications systems. The first cellular telephone systems were analog systems that operated in a frequency band from around 800 MHz to 960 MHz. Newer, digital communication systems operate in PCN or PCS networks at higher frequency bands of between about 1500 to about 2400 MHz. The frequency bands have been expanded for currently, the cellular frequencies for most North American cellular systems include two frequency bands: 824-894 MHz for the AMPS band and 1.85-1.99 GHz for the PCS band. In Europe these two bands are slightly different and include 890-960 MHz for GSM and 1.71-1.88 GHz for the PCN band, with some communication frequencies being as high as 2.17 GHz.
Systems that operate in both these bands are preferred so that communication can be supplied to a system user regardless of the equipment the user or system operates. In order to complement the operation of the system, it is desirable to efficiently couple a system antenna to the telephone or other apparatus. A coupler is a device that is used to couple radio-frequency (RF) signals between two components of a system, such as in a mobile telephone system, the exterior antenna and the interior coaxial cable and vice-versa. The couplers permit window mounting, and are mounted on opposite sides of a mounting surface which is typically a portion of one of the windows of a vehicle.
Typically, these couplers are structured to operate only in a single narrow frequency band. Other couplers, such as that described in U.S. Pat. No. 6,069,588, issued May 30, 2000 are complex in structure because they utilize multiple electronic components as part of the coupler. Still other couplers, like that described in U.S. Pat. No. 5,995,821 issued Nov. 30, 1999 uses multi-part coupling elements that must be oriented at desired angles and distances to each other in order to efficiently operate. In order to accommodate cellular and mobile telephones that operate in multiple cellular bands, a coupler itself must be capable of transferring RF signals through the medium upon which it is mounted with minimal signal loss.
A need therefore exists for an improved coupler that operates efficiently in multiple frequency bands with a simple structure, and which has minimal signal loss in operation. The present invention is directed to such a coupler.
It is therefore a general object of the present invention to provide an improved coupler that operates within dual frequency bands of wireless communication systems.
It is another object of the present invention to provide a simple and inexpensive coupler that efficiently couples RF signals in a wide bandwidth of from about 800 to about 2000 MHz.
It is yet another object of the present invention to provide an improved coupler for use with wireless telecommunication systems that includes a bowtie slot formed within a layer of conductive material on the surface of a circuit board and which is fed from a feedline on the opposite side of the circuit board, the feeding occurring at the apex of the bowtie.
Still another object of the present invention is to provide an improved dual band-operative coupler of small size that encompasses all present bands of cellular communication frequencies and that includes a pair of dielectric bases adapted for respective attachment to opposite sides of a glass surface of either a vehicle or building, the bases having opposing first and second sides, the second sides of the bases each including a layer of conductive material disposed thereon, and, a pair of bowtie slots formed thereon in alignment with each other so that one bowtie slot is located within the other bowtie slot, the two bowtie slots being separated from each other by an intervening layer of conductive material, each base further including a feed point that provides a feed point providing a feed connection through the dielectric stratum to the apexes of the two bowties.
Yet a still further object of the present invention is to provide a coupler incorporating a pair of bowtie-shaped slots of the structure set forth above and further including a tuning network extending along an opposite surface of the support and connecting to the bowtie element(s) at an associated apex portion thereof.
The present invention accomplishes these objects and advantages through its novel and unique structure. In one principal aspect of the present invention, a coupling element is provided for attachment to an interior surface of a vehicle or building, preferably a window. The coupler includes a housing, a coaxial transmission line and a dielectric support board disposed within the housing. One side of the board that faces toward the interior surface of the window has a layer of conductive material formed thereupon. A pair of slots are formed in the conductive material, in the form of inner and outer slots. The outer slot has the shape of a bowtie in which a pair of triangular-shaped members are joined together at their apexes. The inner slot also has the shape of a bowtie and the inner slot is separated from the outer slot by an extent of conductive material. The two bowtie slots are preferably oriented along common axes, and the intervening conductive layer that separates them from each other also has a bowtie shape, or a shape that approximates an angled lemniscate. The first and second bowties are separated at their apexes by the opening. The other side of the dielectric board supports the transmission line which is terminated to the coupler by way of a passage, or via, that extends through the board and which communicates with the apex of the bowtie.
In another principal aspect of the present invention, the transmission line may be terminated to a conductive tuning network disposed on the opposite side of the dielectric board. This network may include a serpentine pattern of conductive material, such as foil that may be arranged to provide the desired frequency. The bowtie pattern can be easily formed on the dielectric boards by etching the conductive material disposed on the surfaces thereof. Conventional circuit board material may be used for the substrate such as phenolic, copper-clad or laminated sheets or epoxy-based or fiberglass fabric sheets coated with a conductive layer.
These and other objects, features and advantages of the present invention will be clearly understood through consideration of the following detailed description.